[SB] Remove SignalCallback#setCallIndicator & associated methods.

SignalController#notifyCallStateChange was the only class invoking
SignalCallback#setCallIndicator, but #notifyCallStateChange is never
actually called. So, this CL removes #notifyCallStateChange,
setCallIndicator, and any other associated methods and classes.

Bug: 291321279
Flag: EXEMPT dead code removal
Test: compiles
Test: atest StatusBarSignalPolicyTest StatusBarIconControllerImplTest
Change-Id: I8eb41612d32ff55b17cba1931f0f754ba9a22ad2